Better introspection functions: info/repr

[vidartf]

Currently, the info() method of container / dict traits only use the default Instance implementation, leading to rather uninformative information when there are restrictions on the elements, e.g. with a complex structure along the lines of:

trait = Tuple((
    CFloat(33),
    Unicode('default', allow_none=True), 
    List(Int(0), min_length=3),
))

the info string will simply be 'a tuple'.

Separately, it would be nice if the base trait types included a __repr__, so that a trait could be introspected without having to refer to the source (especially useful for traits constructed dynamically).